An earth-boring drill bit is typically configured on the lower end of a drill string and is rotated by rotating the drill string at the surface or by actuation of downhole motors or turbines, or by both methods. With weight applied to the drill string, the rotating drill bit engages the formation and proceeds to form a borehole along a predetermined path toward a target zone.
A typical earth-boring bit includes one or more rotatable cutters that perform their cutting function due to the rolling movement of the cutters acting against the formation material. The cutters roll and slide upon the bottom of the borehole as the bit is rotated, the cutters thereby engaging and disengaging the formation material in its path. Cutters are generally of two types: composite inserts formed from a hard material such as tungsten carbide cemented with a binder such as cobalt, or milled teeth formed as extensions protruding from the surface of the roller cone.
The cost of drilling a borehole is proportional to the length of time it takes to drill to the desired depth and location. In oil and gas drilling, the time required to drill the well, in turn, is greatly affected by the number of times the drill bit must be changed in order to reach the targeted formation. This is the case because each time the bit is changed, the entire string of drill pipe, which may be miles long, must be retrieved from the borehole, section by section. Once the drill string has been retrieved and the new bit installed, the bit must be lowered to the bottom of the borehole on the drill string, which, again must be constructed section by section. This process, known as a “trip” of the drill string, requires considerable time, effort and expense.
To keep costs down, it is important that the drill bit fails as few times as possible while drilling a borehole. One such cause of drill bit failure is worn or broken cutting inserts. Cutting inserts may fail by either becoming excessively worn, so that the formation is no longer effectively drilled, or by breaking off, wherein the pieces of broken insert contact the roller cone, potentially leading to roller cone failure. Whether becoming excessively worn, or breaking off, insert failure can be attributed to either surface or internal flaws of the insert. Because repairing broken inserts and roller cones is costly and time consuming, significant modifications have been made to the design and manufacturing processes of inserts.
One manufacturing process to improve the strength and life of cutting inserts involves the vibratory finishing of the cutting inserts prior to their press-fitting into the roller cone of a drill bit. During vibratory finishing, inserts are moved in a vibratory bowl or barrel shaped vibrating machine where they constantly contact media and one another. The insert on insert contact, along with the insert on media contact smoothes the surface of the inserts, thereby reducing insert flaws on the cutting inserts. A process disclosing the finishing of inserts in a vibratory finisher is described in U.S. Pat. No. 4,869,329 issued on Sep. 26, 1989 to Kar, hereby incorporated by reference herein. The Kar patent teaches using increased time to improve the toughness of inserts by extending the vibratory tumbling or finishing operations thereon. While the process of vibratory finishing has increased the toughness of inserts, the advantages gained as a result of longer tumbling times are confined to the reduction of the size and distribution of surface flaws due to the limited amount of velocity and/or energy generated by this method.